Marine biofouling imposes significant operational and ecological costs for the maritime industry, including increased hydrodynamic drag, material degradation, and the spread of non-native species. This study investigated the use of cayenne pepper to reduce fouling on submerged hard substrate - a method sometimes used by recreational boat owners for anti-fouling and referred to as "Cajun coating." We ran a preliminary short-term efficacy study to evaluate whether capsaicin, the active ingredient in cayenne pepper, enhances the effectiveness of traditional copper-based antifouling coatings under in-situ conditions. Fiberglass-coated tiles were assigned six treatments (copper only, copper with 0.5%, 1%, or 2% capsaicin, copper plus methylated seed oil, and an uncoated tile control) and were deployed in the marine environment for six weeks in coastal Alabama. Nine taxa were recorded, with taxa richness highest on controls and lowest on 2% capsaicin tiles. Community composition differed significantly among treatments, with soft-bodied taxa (e.g. soft tube-dwelling polychaetes, hydroids) declining in response to capsaicin, whereas barnacles showed minimal response. Detritus and bare space generally increased with capsaicin concentration. Notably, bare space - perhaps the most relevant indicator of antifouling efficacy - was significantly greater in the 2% capsaicin treatment than in the copper treatments, indicating enhanced antifouling performance with incorporation of capsaicin. Largest differences were also seen between 1% and 2% capsaicin treatments, particularly in total mean taxa abundance and percent detritus. Overall, capsaicin enhanced antifouling performance in a concentration-dependent manner, particularly against soft-bodied taxa and increasing bare space, suggesting this approach has potential as an environmentally benign antifouling option. Our results provide preliminary in-situ research-based evidence for this low-technology and cost-effective approach to reduce marine biofouling on infrastructure and recreational vessels.
Biofilms show an enhanced tolerance to antimicrobials compared to planktonic cells and conventional susceptibility tests provide limited insight into antibiotic action within intact biofilms. We assessed swept-source optical coherence tomography (SSOCT) as a non-destructive, label-free platform for biofilm monitoring, extracting two label-free parameters, the optical attenuation coefficient (mu(t)) and biospeckle temporal contrast (gamma). Biofilms cultured for 24 h, were treated with antibiotics at minimum biofilm eradication concentration (MBEC) determined by the Calgary biofilm device and imaged at 0, 24 and 48 h post-treatment alongside time-matched untreated controls, with parallel colony forming unit (CFU) enumeration. Untreated biofilms showed progressive increases in both mu(t) and gamma, confirming that time-matched rather than pre-treatment controls are required. Treated biofilms showed elevated mu(t) (76.9-103.2% above control, p < 0.001) but declining gamma (68.4% and 68.6% below control at 48 h, p < 0.001), with the mu(t)-gamma correlation reversing from positive during maturation (r = +0.93) to negative under treatment (r = -0.94). Viable counts decrease by similar to 2.5 log(10) CFU/mL in both treated arms (p < 0.001), confirming substantial killing; gamma nonetheless declined nonlinearly with respect to viability and continued falling after CFU/mL stabilized, indicating that gamma reflects progressive physical quiescence rather than viable cell numbers. SSOCT attenuation and biospeckle thus offer a non-destructive complement to conventional viability assays.
Marine biofouling on ship hulls substantially increases hydrodynamic drag and operational costs. This study selects the barnacle, a sessile crustacean with strong adhesion ability, and develops polydimethylsiloxane films patterned with micro-cylinders to achieve dual-functional antifouling and drag reduction based on the barnacle larvae dimensions and hydrophobic principle. Bioassays with barnacle cyprid larvae demonstrated that the microstructured surfaces significantly inhibited settlement, achieving an antifouling rate of 59%. Rotational drag tests further revealed a maximum drag reduction of 7.2% at 100 rpm. To elucidate the physical mechanisms, computational fluid dynamics simulations using the volume of fluid model were conducted. The numerical results verified the stability of the entrapped gas-liquid interface within the microstructures and revealed a substantial reduction in near-wall turbulence intensity and shear stress, quantitatively validating the slip-effect mechanism. These combined experimental and numerical results demonstrate the potential of engineered microstructured surfaces for marine antifouling and drag reduction applications.
